There are a variety of therapies or treatment modalities that require a catheter with a distal anchor or the like to retain the catheter in position. One particular application involves catheters used for drainage purposes. Generally, these catheters are introduced into a patient through a large hypodermic needle or trocar. A guidewire is inserted through the needle or trocar which is then removed. The catheter tube, with a stiffening cannula, passes over the guidewire into the cavity. The cannula and guidewire can then be withdrawn leaving a portion of the catheter at its distal end in the desired cavity.
Various catheters have been developed with diverse anchor structures to prevent inadvertent removal of the catheter. Referring now to FIG. 1, one such anchor comprises a “pigtail loop” configuration 100 (shown in dashed lines) of distal flexible tube portion 102 at or near the distal end of catheter 104. The pigtail loop configuration 100 of portion 102 is also referred to herein as a “closed” configuration. Portion 102 also has an open configuration 101, shown in solid lines in FIG. 1, in which the portion is straight rather than curved. Portion 102 has a number of ports 106 to ensure drainage. The pigtail loop configuration 100 prevents accidental removal of the catheter from the patient. Generally pigtail loop 100 is preformed in the catheter because the flexible tube of the catheter is formed of a memory material. For introduction into a patient, a stiff cannula (not shown) or similar implement is inserted through the catheter lumen 108 to straighten the pigtail loop. The distal end of the flexible tube returns to the pigtail loop configuration after the cannula is removed. Typically a suture thread 110, thin cable, or other filamentary member extends through draw ports 106a and 106b at two spaced positions along the distal portion of the flexible tube. The term “suture” as used herein throughout for simplicity to refer to the filamentary member does not imply any limitation to the type of filamentary member. These ports come into juxtaposition when the pigtail loop 100 forms after the physician removes the cannula. Then the physician will take up any slack in suture 110 that leads proximally from pigtail loop 100. When suture 110 is made taut, it holds the juxtaposed ports 106a and 106b of the catheter together and thereby prevents the pigtail loop from straightening. If only a portion of suture 110 is drawn proximally, the suture will still prevent the pigtail loop from straightening completely.
When it is appropriate to remove the catheter, a stiff cannula is inserted through the lumen 108 with suture 110 still taut until the cannula reaches pigtail loop 100. The tension in suture 110 minimizes the chances for the cannula entangling with the filamentary member. Thereafter the tension on suture 110 is released before or while the stiff cannula is advanced distally to straighten the pigtail loop and facilitate the removal of the catheter from the patient.
A number of structures or “controllers” are known in the art for taking up the slack in suture 110, some of which are twist-locking designs by which axial rotation of a barrel at the end of the catheter causes tightening of the filamentary member. U.S. Pat. No. 5,419,764 to Roll and U.S. Pat. No. 6,042,577 to Chu et al., both incorporated herein by reference, disclose exemplary structures incorporating twist locks. U.S. Pat. No. 5,941,849 and a continuation thereof, U.S. Pat. No. 6,231,542, by Amos, Jr. et al., both of which are assigned to the assignee of the present invention and incorporated herein by reference, disclose several other controller designs.
More details of an exemplary controller 10 are shown in FIGS. 2A–2C. Controller 10 comprises a spindle 12 that fits radially over catheter 11, strain relief 13, end cap 14 having a notch 15 to allow it to snap onto the spindle, threaded washer 16 that is split for installation over the spindle, O-ring 17 that fits in a channel defined by proximal shoulder 18a and distal shoulder 18b, winding washer 19, and hub 20. Internal threads in hub 20 (not shown) allow hub to be twisted on threaded washer 16, the eight flanges 21 on winding washer 19 interlocking with the octagonal periphery of hub 20 to rotate the winding washer in concert with the hub. Hub 20 comprises an integral luer connection 24. Suture 110 is threaded through port 25 communicating between an inner lumen 109 in spindle 12 and the outer surface 26 of the proximal end 27 of spindle 12. The proximal end of suture 110 is attached to the winding washer through holes 23. Thus, twisting hub 20 about spindle 12 on threaded washer 16 twists the winding washer by engagement of the polygonal inner periphery of the hub with the outer periphery of the washer, to helically wind the suture about the outer surface 26 of spindle proximal end 27, taking up the slack in the suture.
Threaded washer 16 is mounted on a flattened portion 22 of spindle 12 having a non-round cross-section, as shown in FIG. 2C, but is free to move axially when hub 20 is rotated. Thus, rotation of hub 20 does not cause the hub to move axially, but rather moves threaded washer 16 axially, as described in more detail in the '849 and '542 patents. End cap 14 and distal shoulder 18b of the channel for O-ring 17 create the proximal and distal axial boundaries respectively for movement of threaded washer 16.
The '849 and '542 patents further disclose embodiments wherein the pitch of the threads on washer 16 is chosen so that the fully closed pigtail configuration of 100 and fully open configuration 101 coincide with the threaded washer abutting the corresponding axial boundaries. In practice, however, it has proven preferable for the axial boundary of travel for washer 16 at end cap 14 not to coincide with the fully closed pigtail configuration 100. In part, this is because it is preferred for a single controller design to be used with different pigtail sizes, which would require different threaded washers and mating hubs to be provided in the controller for each size pigtail.
Thus, controller 10 shown in FIGS. 2A–2C lacks means for indicating to the practitioner when the pigtail is fully closed. Consequently, practitioners tend to stop twisting based on the amount of resistance that they feel. This may lead to undertwisting or overtwisting, both of which may have adverse consequences. Undertwisting may result in the pigtail not being fully closed, which, if the catheter is not firmly anchored, may cause the catheter to become dislodged and fall out. Overtwisting may stress the filamentary member to the point that it snaps, requires removal of the catheter and replacement with a new one. Thus, there is a need in the art for drainage catheters that can indicate closure of the anchor mechanism.
Strain relief 13 as shown in FIGS. 1–2B comprises a flexible, releasable tubular section 28 shown in rolled configuration 29A in FIG. 2A and in dashed lines in FIG. 2B, and in a fully extended configuration 29B (solid lines) in FIG. 1 and FIG. 2B. When tubular section 28 is unrolled in the fully extended configuration 29B, it prevents rotation of hub 20 relative to spindle 12 because of the frictional resistance to rotation of strain relief 13 on spindle 12. Although this may prevent a patient from unintentionally twisting hub 20 and loosening suture 110, which would have the effect of undoing pigtail 100, controller 10 shown in FIGS. 1–2C lacks any means to prevent patients from intentionally doing so. Thus, a motivated patient may merely unroll portion 28 and then freely twist hub 20. Furthermore, the frictional resistance between strain relief 13 and spindle 12 may be overcome with sufficient force. Thus, there is also a need in the art for drainage catheters that can prevent intentional and/or unintentional unlocking of the catheter when in the closed configuration.